Combined test that evaluates two FGF4 retrogene insertions associated with skeletal phenotypes and with the risk of intervertebral disc herniation in the dog. The insertion on chromosome 18 (CDPA) determines the shortened limbs typical of many breeds; the insertion on chromosome 12 (CDDY) is associated with chondrodystrophy and an increased risk of degenerative disc disease (IVDD). It is a test that cuts across most breeds, not limited to a single one.

FGF4 insertions are widespread in chondrodystrophic breeds (Dachshund, Beagle, Basset, Shih Tzu, etc.) and present in many other breeds, including medium and large ones. Frequencies are high in breeds with a short-legged phenotype; for CDDY-IVDD the clinical risk varies by breed and line.

- Shortened limbs (CDPA phenotype)\n- Elongated body and short limbs in chondrodystrophic breeds\n- Increased risk of thoracolumbar disc herniation (CDDY-IVDD phenotype)\n- Back pain and cervicalgia\n- Paresis and paralysis due to acute spinal cord compression\n- Reduced or absent nociceptive reflex in the pelvic limbs in severe hernias

The FGF4 retrogene insertions were characterised around 2017 by the group of H. Bannasch. Two independent retrotransposon insertion events were identified, one on chromosome 18 responsible for chondrodysplasia (CDPA) and another on chromosome 12 associated with chondrodystrophy and risk of disc herniation (CDDY-IVDD). The finding explained the genetic basis of the short-legged phenotype present in many canine breeds and provided a disc risk marker of great clinical utility.

- Test breeding animals to determine CDPA and CDDY-IVDD status.\n- In breeds whose standard requires short limbs, CDPA is phenotypically desired; it does not require automatic exclusion.\n- For IVDD risk, apply a dose-dependent criterion: avoid the combinations with the highest number of CDDY copies in breeds with a high incidence of disc herniation.\n- Combine the result with weight control, appropriate exercise and jump management.\n- Do not remove animals solely because of CDPA status where the phenotype is standard.

Differential diagnosis of the acute neurological picture with trauma, neoplasms and discospondylitis. MRI is the test of choice to assess spinal cord compression. The genetic result guides the risk but does not replace the clinical assessment of the patient with pain or neurological deficit.

1. Brown EA et al. 2017, el retrogén FGF4 en CFA12 es responsable de la condrodistrofia y la enfermedad del disco intervertebral en perros (PMID 29073074)
2. Batcher K et al. 2020, múltiples retrocopias de FGF4 derivadas recientemente en cánidos (PMID 32717834)
3. Tellegen AR et al. 2019, el perro como modelo de osteoartritis: la inserción del retrogén FGF4 (PMID 31373395)
4. OMIA:001349 Condrodisplasia (CDPA) / OMIA:001350 Condrodistrofia (CDDY)